In recent years, biodegradable plastics have been actively developed as materials that can solve problems caused by the heavy burden of plastic waste on the global environment, such as harmful effects on the ecosystem, generation of harmful gas during combustion, and global warming due to a large amount of heat generated by combustion.
Particularly, carbon dioxide generated by combustion of plant-derived biodegradable plastics was originally present in the air. Therefore, combustion of plant-derived biodegradable plastics does not increase the amount of carbon dioxide in the atmosphere. This is referred to as “carbon neutral”, and is regarded as important under The Kyoto Protocol that sets targets for reducing carbon dioxide emissions. Therefore, active use of plant-derived biodegradable plastics is desired.
Recently, from the viewpoint of biodegradability and carbon neutral, aliphatic polyester-based resins have received attention as plant-derived plastics. Particularly, polyhydroxyalkanoate (hereinafter, sometimes referred to as PHA)-based resins have received attention. Among PHA-based resins, poly(3-hydroxybutyrate) homopolymer resins (hereinafter, sometimes referred to as P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer resins (hereinafter, sometimes referred to as P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer resins (hereinafter, sometimes referred to as P3HB3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymer resins, polylactic acid, etc. have received attention.
However, it is known that the PHA-based resins are slow in crystallization. Therefore, the PHA-based resins require a long cooling time for solidification after heat-melting in molding processing, which causes problems such as poor molding processability and poor productivity.
Therefore, blending of a PHA-based resin with an inorganic material such as boron nitride, titanium oxide, talc, lamellar silicate, calcium carbonate, sodium chloride, or metal phosphate has heretofore been proposed to promote crystallization. However, the blending with an inorganic material has many adverse effects on a resulting molded article, such as reduction in tensile elongation and poor appearance, and is therefore poorly effective.
PTL 1 discloses that blending of a PHA-based resin with an amide bond-containing compound promotes the crystallization of the PHA-based resin. However, further improvement is desired to improve productivity.